Essay --

Investigating the effect of caffeine concentration on the heart rate of Daphnia Introduction Daphnia, commonly known as water fleas, are tiny crustaceans which live in water. The diameter of adult female bodies is approximately 3-5 mm. The upper skeleton is transparent, making the internal organs visible. This allows the heart rate of the Daphnia to be calculated by observing them under a microscope. Background Caffeine occurs naturally in some plants such as coffee beans and tea leaves. Caffeine is also added to other beverages. Beverage containing caffeine (100ml) Amount of caffeine (mg) Caffeine per 1ml of beverage Coffee 55 0.55mg Tea 35 0.35mg Coca Cola 15 0.15mg Caffeine is medically known as trimethylzanthine. Caffeine acts as a cardiac stimulant which means that it increases heart rate. Adenosine is a natural chemical found in the body which binds to respective adenosine receptors in the sinoatrial node and slows down the activity of the nerve cells. Caffeine also binds to these receptors which results in the activity of these nerve cells to increase. Caffeine consumption also causes the adrenaline hormone to be released into the body, further increasing the speed of bodily functions. Caffeine also constricts blood vessels which is why some headache medicine and painkillers contain sources of caffeine. 2 cups of strong coffee has been shown to increase heart rate in humans by about 15 beats per minute. Hypothesis As the caffeine concentration increases, so does the heart rate of the daphnia. Prediction The prediction for this experiment is that the higher the concentration of the caffeine, the higher the heart rate in beats per minute. This is because caffeine acts as a stimulant, causing the adrenaline hormone b... ...d by the lamp being on cannot be easily controlled and could be a factor for the increasing heart rate. The heart rate may also increase as a result of the efforts of the Daphnia in escaping from the cavity slide due to limited water supply. Conclusion The results of the experiment indicate that the initial hypothesis was acceptable as the higher the caffeine concentration, the higher the heart rate of the Daphnia. The results do not show this link in all cases; this could be down to temperature rise because of the heat produced by the microscope lamp, leading to the heart rate of the Daphnia increasing. This could explain the results for the 0.2% caffeine concentration. To improve the accuracy of the results, the same person should conduct all of the experiments as different people may count the heart rate at different speeds, leading to variation in the results.